How to do string concatenation in Oracle stored procedure

In Oracle database, a stored procedure is a programmed code unit that can be called and execute a series of programs. Stored procedures allow complex operations on the database and can also receive parameters. Among them, string splicing is a very common requirement. This article will introduce how to perform string splicing in Oracle stored procedures.

Generally, when we write SQL scripts, we use the "||" operator to complete string concatenation. However, in stored procedures, using the "||" operator may cause additional overhead. Therefore, Oracle provides another way to perform string concatenation: using the "CONCAT" function.

The "CONCAT" function can splice two or more strings together and return the splicing result. Below is an example of string concatenation using the "CONCAT" function:

DECLARE
    name_1 VARCHAR2(20) := 'John';
    name_2 VARCHAR2(20) := 'Smith';
    full_name VARCHAR2(50);
BEGIN
    full_name := CONCAT(name_1, ' ', name_2);
    DBMS_OUTPUT.PUT_LINE('Full name is: ' || full_name);
END;

In the above code, we define two string variables "name_1" and "name_2" and use the "CONCAT" function Piece them together. Finally, we save the spliced ​​result in the "full_name" variable and use the "DBMS_OUTPUT.PUT_LINE" function to output the result to the console.

In addition to using the "CONCAT" function, you can also use the "||" operator to complete splicing. However, it should be noted that using the "||" operator in a stored procedure may cause additional overhead. To avoid this situation, we can use the "CONCAT" function provided by Oracle.

In addition, if we need to concatenate a set of strings into one large string, we can use the "LISTAGG" function. The following is an example of using the "LISTAGG" function for string concatenation:

DECLARE
    type_list VARCHAR2(4000);
BEGIN
    SELECT LISTAGG(type_name, ',') WITHIN GROUP (ORDER BY type_name)
    INTO type_list
    FROM type_table;
    DBMS_OUTPUT.PUT_LINE('Type list is: ' || type_list);
END;

In the above code, we define a variable "type_list" and use the "LISTAGG" function to concatenate the The "type_name" fields are concatenated together. Finally, we save the spliced ​​results in the "type_list" variable and use the "DBMS_OUTPUT.PUT_LINE" function to output the results to the console.

When using the "LISTAGG" function, you need to pay attention to the following two issues:

1. The length of the concatenated string cannot exceed the maximum length of the VARCHAR2 type (4000).
2. If the number of spliced ​​strings is too large, it may cause the error "ORA-01489: The result set is too large". In this case, you can use the "XMLAGG" function to solve it.

In summary, to perform string splicing in Oracle stored procedures, we can use the "CONCAT" function or the "LISTAGG" function. Both methods can complete string concatenation, but it is more efficient to use different methods in different scenarios.

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